1. Field of the Invention
The present invention relates to a novel carboxylate and a heat-sensitive recording material using the same. More specifically, the present invention relates to a heat-sensitive recording material which is excellent in the stability of a color image and which has absorptions in both the visible region and near infrared region.
2. Description of the Prior Art
In recent years, extensively prevalent heat-sensitive recording materials permit the easy formation of sharp color images by the use of a simple device, and for this reason, these recording materials have widely been put to practical use as papers for facsimiles and word processors, chart papers for various kinds of analyzers, tickets, commuter passes, prepaid cards, tags and the like. However, it is well known that these heat-sensitive recording materials, in which phthalide-based and fluoran-based leuco-pigments are used, have a problem that the stability of the color images is poor. In other words, these recording materials have a drawback that the color of the color images fades due to sunlight and the light of a fluorescent lamp, alcohol contained in a cosmetic, plasticizers contained in resin films or a plastic erasers, and the like.
Nowadays, the development of the facsimiles using plain papers has rapidly advanced, so that this field, in which the heat-sensitive recording papers have been most largely used, begins to be invaded. Therefore, the demand for the enhancement of the stability of the color images has been remarkably increased. Thus, in order to solve this problem, various investigations have been made.
One of these investigations is a trial that a metallic phthalocyanine is produced by a thermal reaction between a phthalocyanine precursor and a metallic salt. For example, in Japanese Patent Publication No. 8357/1983, 1-amino-3-iminoisoindolenine or its derivative and a metallic salt of an organic acid or a metal complex compound are used in a heat-sensitive layer. However, this heat-sensitive layer is poor in sensitivity, and there is also a problem that the metallic compound has a bad influence on the environment.
Furthermore, Japanese Patent Publication No. 16353/1992 discloses a recording material on which an imino compound such as 1,3-diiminoisoindoline is supported. However, it has been found that this diiminoisoindoline compound generates an ammonia gas in water to decompose into a phthalimide compound or an monoamide compound of an orthodicarboxylic acid. It has been understood that the diiminoisoindoline compound alone having 4 chlorine atoms in a benzene ring can be used for coating in an aqueous system, but the recording material using this compound has not developed any color, even when heat has been applied at 200.degree. C. for 10 seconds.
Japanese Patent Publication Nos. 38995/1991 and 38996/1991 disclose heat-sensitive recording materials obtained by utilizing the reaction between an aromatic isocyanate and 1,3-diimino-4,5,6,7-tetrachloroisoindoline which does not decompose even when dispersed and coated in an aqueous system. These disclosed techniques have some defects, and for example, a color development sensitivity is still low, and the storage stability of the backgrounds of the heat-sensitive recording materials is also poor due to the aromatic isocyanate.